Ignition timing control for piezoelectric engine ignition systems



Aug. 1965 D. w. FELDMAN 73 IGNITION TIMING CONTROL FOR PIEZOELECTRIG ENGINE IGNITION SYSTEMS Filed March 9, 1962 El 2/ f zo Z 2 3/ g A .0'5.|'045320325303540.4550 sEpARAnou m INCHE5 INVENTOR.

"HZ DANIEL W. FELDMAN Mi /M ATTORNEYS.

3,202,873 IGNITION TIMING CONTROL FOR PIEZO- ELECTRIC ENGINE IGNITKON SYSTEMS Daniel W. Feldman, Shaker Heights, hio,,assign0r to The Standard Oil Company, Cleveland, Ohio, a corporation of Ohio Filed Mar. 9, 1962, Ser. No. 178,670 1 Claim. (Cl. 315209) This application relates to internal combustion engine ignition timing.

Piezoelectric ignition systems for internal combustion engines have been introduced which produce the high voltage necessary for spark ignition by the application of a compressive stress to a ceramic piezoelectric material. For increasing the service life of the ceramic material by the avoidance of shock loads, the compressive force is increased over'a finite time with the production of a gradually increasing voltage. If the sprak plug is connected directly to the piezoelectric ignition generator the timing of the spark .plug firing depends upon the voltage requirement of the plug which tends to vary with wear, deposits, .and any "other operating variables.

In accordance with the invention, means are employed lfOl' avoiding variability in timing. In carrying out the invention in its preferred form, a calibrated air-gap is introduced in series between the piezoelectric voltage generator and the spark plug allowing the ignition spark to fire only at the precise time the voltage value of the series gap is reached. The electrode separation of the calibrated air-gap is such as to provide a breakdown voltage equal to a plurality of times that of the spark plug. The change in pressure on the piezoelectric ceramic voltage generator varies in fixed relation to the crank shaft or the cam shaft of the engine and consequently the voltage also varies in fixed relation to the position of the cam shaft. Thus, the use of a calibrated air-gap result-s in the attainment of a voltage sufiicient .to produce breakdown and engine ignition in predetermined time relation to the position of the pistons connected to the crank shaft.

A better understanding of the invention will be afiorded by the following detailed description considered in conjunction with the accompanying drawing, in which:

FIG. 1 is a graph illustrating the linear relationship between minimum air-gap voltages and between electrode separation in the calibrated air-gap;

:FIG. 2 is a schematic diagram of an engine ignition system embodying the invention;

FIG. 3 is a diagrammatic representation in perspective of a packaged calibrated air-gap constituting an embodiment of the invention;

FIG. 4 is .a sectional view of the gap of FIG. 3; and

FIG. 5 is a view of a spark plug formed with a shank containing a calibrated air-gap in accordance with the invention.

Like reference characters are utilized throughout the drawing to designate like parts.

The use of the calibrated air-gap obviates the necessity for a timing switch, but if desired for multi-cylinder engines a distributor may .be employed.

In ignition systems for internal combustion engines employing voltage generators of the piezoelectric ceramic type an eccentric or a earn 1 is provided, mounted upon the drive shaft or an extension of the cam shaft of the engine (not shown) for applying repetitive compressive stress to ceramic piezoelectric material consisting of blocks 2 and 3, by means of the lever 4 of a force multiplication system.

In accordance with one embodiment of the invention, .a calibrated air-gap 5 is connected through a distributor 6 to a spark plug 7. It will be understood that other 'United States Patent 0 spark plugs for engines having more than one cylinder "ice Patented Aug; 24, less (not shown) may be connected in other positions of the distributor 6. p

The ceramic voltage generator, that port-ion of the apparatus, enclosed within the dashed line rectangle 11 does not constitute a part of the present invention, but may take the form of a spark pump such as manufactured by the Clevite Corporation and described in patents, Nos. 3,006,857 and 3,009,975.

The arrangement described makes it unnecessary to employ 'a timing switch handling high Voltage pulses. The rotating arm of the distributor 6 and the cam 1 are so connected in angular relation to each other upon a common shaft that the rotating arm of the distributor 6 reaches the circuit-connecting position for one of the engine cylinders before the cam 1 reaches the-position applying suflicient stress to the ceramic blocks 2 and 3 to produce a voltage which will breakdown the calibrated air-gap 5. However, the distributor electrode is broad enough to retain circuit connection while the voltage is building up. Consequently, the distributor 6 is not required'to handle high voltage in closing or opening and the timing is effected entirely by'the calibration of the calibrated air-gap 5. As a result, neither the distributor 6 nor any other part of the system is vulnerable to internal shunting caused by the deposition of moisture or the accumulation of dust, and so forth, which causes trouble in high voltage circuits.

As more fully described in the cited patents, the ceramic blocks 2 and 3 are of the lead-zirconate-titanate type of piezoelectric ceramic. The ingredients may be in the [following proportions:

Lead-zirconate and lead-titanate in mole ratio 60:40 to 45:55, with 020 atomic percent of calcium or strontium and 0.1 to 1.5 weight percent chromium or uranium oxide.

The blocks 2 and 3 are cemented to terminal plates 12 and 13, each of which is in turn cemented to a terminal conductor 14 at which the high voltage appears when the blocks 2 and 3 are vfully stressed. It will be understood that the ends 15 and 16 of the blocks 2 and 3 may be at ground potential or the potential of the motor vehicle frame.

The requisite separation of the electrodes of the calibrated air-gap 5 depends upon the parameters of the internal combustion engine employed. Generally speaking, the best results are obtained inthe range between 14,000 and 18,000 volts produced by electrode separations be tween .18 and .25 as indicated in the graph of FIG. 1. However, satisfactory operation may be obtained in various engines at higher or lower voltage settings such as,

for example, between 5,000 and 25,000 volts represented by electrode separations of .07 and .35" of graph of FIG. 1. These voltages are well above those required for resistance to spark-plug fouling.

If desired, the calibrated air-gap may take the form of a packaged unit which may snap onto the conductor 14 from the voltage generator and onto the top terminal of the spark plug 7 or on to the distributor terminal in (case a distributor 6 is employed.

The packaged calibrated air-gap illustrated in FIGS. 3 and 4 comprises a capsule 17 composed of a suitable insulating plastic such as polytetrafluorethylene, for example, in which .a pair of electrodes .18 and 19 are molded with a fixed calibrated distance between them projecting into a cavity 21. Preferably, a channel 22 from the cavity is provided to the exterior to prevent build up of pressure.

In the embodiment of FIG. 5 a spark plug 23 is formed having a body 24 of insulating material such as ceramic having a cavity 25 with a channel 26 to the exterior.

A connection is also molded into the body 24 from the electrode 18 to a high voltage terminal 27 of the spark plug. Likewise, a conductor 28 is molded into the body 24 connecting the calibrated gap electrode 19 and the center spark plug electrode 29. It will be understood that as in conventional spark plugs a grounded bent electrode 31 is provided which is connected to the threaded metallic portion 32 of the spark plug.

Certain embodiments of the invention and certain methods of operation embraced therein have been shown and particularly described for the purpose of explaining the principle of operation of the invention and showing its application, but it Will be obvious to those skilled in the art that :many modifications and variations are possible, and it is intended therefore, to cover all such moditications and variations as fall within the scope of the invention.

What is claimed is:

An ignition system for an internal combustion engine having cylinders and pistons movable therein designed for combustion at a predetermined position of the piston in the cylinder; said system comprising a spark plug with electrodes; -a ceramic piezoelectric voltage generating material; a rotatable cam and compression means actuated thereby for subjecting the ceramic material to periodic compression stress and producing an output voltage pulse; a distributor means comprising a rotatable electrode mechanically connected to said cam for synchronous rotation with said compression means and a plurality of stationary electrodes peripherally spaced around the axis of rotation of said rotatable electrode; means connecting said distributor means, said voltage generator, and said spark plug into an electrical series circuit; and a timing means including a calibrated air spark gap means con- References Cited by the Examiner UNITED STATES PATENTS 1,246,735 11/17 Flood n 313-124 1,279,387 9/18 McKernan 313-124 1,400,276 12/21 Flood 313-124 1,484,335 2/24 Kerrigan 315-57 X 1,531,943 3/25 Howard 313-123 X 2,034,170 3/36 Andersen 313-124 2,427,247 9/47= Wilkinson et a1. .315-209 2,473,317 6/49 Webber 313-124 2,573,473 10/51 Mascuoh et al.

2,954,506 9/60 Harkness 315- 3,009,975 11/61 Hufferd et al 315-55 X 3,043,980 7/62 Zalesak 315-58 X DAVID J. GALVIN, Primary Examiner.

JAMES D. KALLAM, JOHN W. HUCK-ERT, Examiners. 

